In the production of natural, leather-like or imitation or artificial leather sheet materials, it is most desirable that such materials have both the appearance and mechanical properties of natural leather. In particular, it is desirable that multi-layered polymeric imitation-leather materials have a break or cockle appearance or a grain-accentuation effect closely resembling that of natural leather. Natural leather often is characterized by appearance of many fine breaks or cracks from the surface thereof which provides a distinct appearance to the leather, and also provides for enhanced mechanical properties, such as better soft-hand properties.
Attempts have been made to provide a more natural leather-like look to imitation-leather materials through bending or crimping imitation-leather materials by various mechanical techniques, such as, for example, by passing the laminate material through a tumbling drum, over a series of breaker bars, or by subjecting the material, where it has a fabric base, to steam and moisture. Other techniques have involved the modification of the chemical properties of the particular polymers used in preparing the imitation-leather material. In some cases, both mechanical and chemical techniques have been employed in an attempt to have the imitation-leather material resemble an outward appearance of natural leather and the mechanical properties thereof.
In one method described in U.S. patent application Ser. No. 656,169, filed Feb. 9, 1976 (now U.S. Pat. No. 4,052,236, issued Oct. 4, 1977), hereby incorporated by reference in its entirety, a process of preparing a polymeric imitation-leather-type material, having an enhanced grain-like surface appearance, is described. In the described process, the laminate material, comprising a base fibrous layer having a continuous coating of a first polymer having a low modulus of elongation, and a second discontinuous coating of a second polymer having a high modulus of elongation, is prepared, which laminate material contains a three-dimensional surface-design effect thereon, typically representing a leather-grain effect, or may be of some other design as desired. The laminate material, which may contain a clear top layer for wear resistance or to enhance the grain, is then flexed to provide a sheet material with an accentuated design effect thereon. Flexing typically is accomplished by subjecting the base of the material to heat and moisture and alternately drying the material, and, thereafter, passing the material through a tumbling drum wherein the material is mechanically flexed, tumbled and crumpled. In this process, both the chemical formulation and the mechanical techniques are employed to obtain an enhanced design effect.
In the described process, the employment of a tumbling drum is not wholly satisfactory, nor is the employment solely of moisture or steam, since there is little, if any, direct control over the degrees of flexing or stretching. A tumbling drum occupies substantial space and consumes energy and often leads to production problems in the continuous feeding into and out of the drum of the laminate sheet material. In addition, there is a desire to control, in a more direct manner, the flexing process, and to provide for a more accentuated grain effect and better mechanical properties; for example, hand properties, in the multilayered laminate material.